Air-conditioning apparatus

ABSTRACT

In plural heat-source-side heat exchangers included in an outdoor unit of an air-conditioning apparatus, bypasses for defrosting are provided with flow-rate adjusting mechanisms for refrigerant flowing into the bypasses. The flow rates of the refrigerant which are to be adjusted by the flow-rate adjusting mechanisms are determined in accordance with ambient environments of plural heat-source-side heat exchangers.

TECHNICAL FIELD

The present invention relates to an air-conditioning apparatus which isapplied to, for example, a multi-air-conditioning apparatus for abuilding.

BACKGROUND ART

When an air-conditioning apparatus performs a heating operation duringwinter season, water vapor in the air adheres to a heat exchanger in aheat source, and frost is formed on the heat exchanger. If the froststill adheres to the heat exchanger, the heating capacity lowers.Therefore, generally, a defrost operation is performed by an outdoorunit during an interval between heating operations to melt the frostadhering to the heat exchanger, to thereby achieve a stable heatingcapacity.

When the defrost operation is performed, the frost formed on the heatexchanger is melted into defrost water, which flows to a lower part ofthe heat exchanger. In a cold region, the temperature of such defrostwater is low, and the temperature of outside air is extremely low.Therefore, in the cold region, in the case where such a defrostoperation is performed in an air-conditioning apparatus, defrost watersometimes refreezes when it flows to a lower part of a heat exchanger.In order to prevent the defrost water from being refrozen, a bypass isprovided at a lowermost part of the heat exchanger, and refrigeranthaving a high pressure and a high temperature is made to flow into thebypass (patent literature 1).

CITATION LIST Patent Literature

Patent Literature: Japanese Unexamined Patent Application PublicationNo. 2006-64381

SUMMARY OF INVENTION Technical Problem

In many cases, as multi-air-conditioning apparatuses for a building,plural air-conditioning apparatuses are used. In this case, outdoorunits of the air-conditioning apparatuses are arranged side by side,that is, they are arranged such that side surfaces of any adjacent twoof them face each other. In the case where plural outdoor units aredensely installed, the distance between side surfaces of any adjacenttwo of the outdoor units is only several centimeters. During the abovedefrost operation, fans of the outdoor units of the air-conditioningapparatuses are stopped, and only outside air thus passes through theoutdoor units. Therefore, in multi-air-conditioning apparatuses, in thecase where plural outdoor units are densely installed, during thedefrost operation, outside air more greatly influences upon front andrear surfaces of the outdoor units than upon the side surfaces of theoutdoor units, which are spaced from each other by a slight distance. Asa result, defrost water tends to refreeze on the front and rear surfacesof the outdoor units.

Also, in many cases, the external shape of an outdoor unit is asubstantially cuboid as a whole. The influence of outside air upon theoutdoor unit varies from one surface of the outdoor unit to anothersurface thereof, since the surfaces of the outdoor unit have differentareas. Furthermore, the temperature of refrigerant at part of the abovebypass which is the farthest from a header of the heat exchanger islower than the temperature of refrigerant at any of the other parts ofthe bypass. Therefore, in a single heat exchanger, the temperature of abypass for preventing refreeze is not uniform over the bypass, adrainage performance is easily worsened, and there is a possibility thatrefreeze will occur, and whether or not refreeze occurs depends on thedistance between part of the bypass and the header.

The present invention has been made to solve the above problem, and anobject of the invention is to improve a defrosting efficiency during adefrost operation in a multi-air-conditioning apparatus in which pluraloutdoor units are installed, and to prevent defrost water from beingrefrozen.

Solution to Problem

An air-conditioning apparatus according to an embodiment of the presentinvention includes: an outdoor unit including a compressor, a flow-pathswitching unit and plural heat-source-side heat exchangers, thecompressor, the flow-path switching unit and the heat-source-side heatexchangers being connected by pipes; and an indoor unit connected to theoutdoor unit to air-condition a target space, wherein the outdoor unitincludes: plural bypasses each having ends one of which is, inconnection by pipes in the outdoor unit, connected to a discharge sideof the compressor, and the other of which is connected to a suction sideof the compressor, the bypasses being configured to cause refrigerant toflow through lower parts of the plural heat-source-side heat exchangersduring a defrost operation of the air-conditioning apparatus; andflow-rate adjusting mechanisms respectively provided in the pluralbypasses to adjust flow rates of refrigerant flowing into the pluralbypasses.

Advantageous Effects of Invention

In the air-conditioning apparatus according to the embodiment of thepresent invention, the plural bypasses configured to cause therefrigerant to flow through lower parts of the plural heat-source-sideheat exchangers during the defrost operation are provided with flow-rateadjusting mechanisms for adjusting the flow rates of the refrigerantflowing into the bypasses. Therefore, in the multi-air-conditioningapparatus for a building, even in the case where the outdoor units aredensely installed, the flow-rate adjusting mechanisms are made tofunction in accordance with the states of the installation of theoutdoor units, whereby defrost water generated during the defrostoperation can be reliably prevented from being refrozen.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram of a refrigerant circuit of anair-conditioning apparatus.

FIG. 2 is a diagram illustrating flows of refrigerant during a heatingoperation of the air-conditioning apparatus.

FIG. 3 is a diagram illustrating flows of refrigerant during a defrostoperation of the air-conditioning apparatus.

FIG. 4 is a schematic diagram of a heat-source-side heat exchanger ofthe air-conditioning apparatus.

FIG. 5 is a diagram illustrating flows of refrigerant in the case wherea solenoid valve for a bypass is opened during the defrost operation ofthe air-conditioning apparatus.

FIG. 6 is a diagram illustrating an example of dense installation ofoutdoor units in embodiment 1 of the present invention.

FIG. 7 is a schematic diagram of a refrigerant circuit of theair-conditioning apparatus according to embodiment 1 of the presentinvention.

FIG. 8 is a control block diagram of the air-conditioning apparatusaccording to embodiment 1 of the present invention.

FIG. 9 is a schematic diagram illustrating heat-source-side heatexchangers in embodiment 2 of the present invention as seen from above.

FIG. 10 is a schematic diagram of a refrigerant circuit of anair-conditioning apparatus according to embodiment 2 of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Refrigeration cycle devices according to embodiments of the presentinvention will be described in detail with reference to the drawings. Itshould be noted that the present invention is not limited to theembodiments, which will be described below. With respect to the figuresto be referred to, there is a case where the size of each of structuralelements is different from that of an actual apparatus.

FIG. 1 is a schematic diagram of a refrigerant circuit of anair-conditioning apparatus. In the air-conditioning apparatus 100,indoor units 10 a, 10 b, 10 c and 10 d are connected to an outdoor unit(heat source unit) 20 by pipes A and B. The indoor units 10 a, 10 b, 10c and 10 d are connected in parallel. The pipes A and B are refrigerantpipes which allow refrigerant (heat-source-side refrigerant) to flowtherethrough.

The outdoor unit 20 includes a compressor 1, a flow-path switching unit2 such as a four-way valve, heat-source-side heat exchangers 3 a and 3 band an accumulator 5, which are connected by pipes. The compressor 1sucks refrigerant, compresses it to cause it to have a high temperatureand a high pressure, and transfers it to a refrigerant circuit. Thecompressor is provided as, for example, an inverter compressor thecapacity of which can be controlled. The flow-path switching unit 2switches the flow of refrigerant between the flow of refrigerant in aheating operation mode and the flow of refrigerant in a coolingoperation mode. The heat-source-side heat exchangers 3 a and 3 bfunction as evaporators in the heating operation mode and function asradiators in the cooling operation mode and a defrost operation mode,and cause heat exchange to be performed between the refrigerant and airsupplied by an air-sending device such as a fan (not shown). Theheat-source-side heat exchangers 3 a and 3 b are connected in parallelby refrigerant pipes in the outdoor unit 20. The heat-source-side heatexchangers 3 a and 3 b are formed in an L-shape as their outer shape,and are arranged to form a rectangular frame as a whole in a housing ofthe outdoor unit 20. The accumulator 5 is installed on a suction side ofthe compressor 1, and accumulates surplus refrigerant which generatesbecause of the difference between the heating operation mode and thecooling operation mode, and surplus refrigerant which generates becauseof a change in a transient operation.

Bypasses 6 a and 6 b are connected to pipes in the outdoor unit 20. Inthe pipes in the outdoor unit 20, one of the ends of each of thebypasses 6 a and 6 b is connected to the discharge side of thecompressor 1, and the other is connected to the suction side thereof.Furthermore, the bypass 6 a extends through lower part of theheat-source-side heat exchanger 3 a, and the bypass 6 b extends throughlower part of the heat-source-side heat exchanger 3 b. Also, thebypasses 6 a and 6 b are connected by pipes to a solenoid valve 4 whichserves as an opening/closing unit. The refrigerant in the pipes does notflow into the bypasses 6 a and 6 b when the solenoid valve 4 is closed,and flows into the bypasses 6 a and 6 b when the solenoid valve 4 isopened. The bypasses 6 a and 6 b and the solenoid valve 4 are used toprevent melted frost from being refrozen after the defrost operation ofthe air-conditioning apparatus 100.

In the indoor unit 10 a, a use-side heat exchanger (indoor-side heatexchanger) 12 a and an expansion unit 11 a are connected in series toeach other. In the indoor unit 10 b, a use-side heat exchanger 12 b andan expansion unit 11 b are connected in series to each other. In theindoor unit 10 c, a use-side heat exchanger 12 c and an expansion unit11 c are connected in series to each other. In the indoor unit 10 d, ause-side heat exchanger 12 d and an expansion unit 11 d are connected inseries to each other. The use-side heat exchangers 12 a, 12 b, 12 c and12 d function as condensers in the heating operation mode, and functionas evaporators in the cooling operation mode, causes heat exchange to beperformed between refrigerant and air supplied by the air-sending device(not shown) such as a fan, and generates air for cooling or air forheating, which is to be supplied to a to-be-air-conditioned space. Theexpansion units 11 a, 11 b, 11 c and 11 d have functions of pressurereducing valves and expansion valves, and reduce the pressure of therefrigerant and expand the refrigerant, and they are also provided as,for example, electronic expansion valves whose opening degrees can becontrolled to be changed. In the air-conditioning apparatus 100, thefour indoor units 10 a, 10 b, 10 c and 10 d are connected in parallel.This, however, is a mere example, and the number of indoor units is notlimited to four.

Each of operation modes of the air-conditioning apparatus 100 will bedescribed.

[Heating Operation Mode]

FIG. 2 is a diagram illustrating flows of refrigerant during the heatingoperation of the air-conditioning apparatus. In FIG. 2, flows ofrefrigerant during the heating operation are indicated by arrows. Thefollowing description is made referring to FIG. 2 with respect to thecase where all the indoor units 10 a, 10 b, 10 c and 10 d are operated.When gas refrigerant having a low temperature and a low pressure issucked into the compressor 1, it is compressed by the compressor 1 tobecome gas refrigerant having a high-temperature and a high andpressure, and is discharged from the compressor 1. The gas refrigerantdischarged from the compressor 1 flows out from the outdoor unit 20through the flow-path switching unit 2 and the pipe A, and flows intothe use-side heat exchangers 12 a, 12 b, 12 c and 12 d.

In the use-side heat exchangers 12 a, 12 b, 12 c and 12 d, the gasrefrigerant having the high temperature and high pressure exchanges heatwith air supplied from the air-sending device not shown, and thusbecomes liquid refrigerant. The use-side heat exchangers 12 a, 12 b, 12c and 12 d function as condensers, which transfer heat to the ambientair, and reduce the temperature of the refrigerant in pipes in the heatexchangers. The liquid refrigerant flows out from the use-side heatexchangers 12 a, 12 b, 12 c and 12 d as liquid refrigerant having a hightemperature and a high pressure, and is expanded and reduced in pressureby the expansion units 11 a, 11 b, 11 c and 11 d to become two-phasegas-liquid refrigerant having a low temperature and a low pressure, andthen the two-phase gas-liquid refrigerant flows from the indoor units 10a, 10 b, 10 c and 10 d. After flowing from the indoor units 10 a, 10 b,10 c and 10 d, the two-phase gas-liquid refrigerant flows into theoutdoor unit 20 through the pipe B. After flowing into the outdoor unit20, in the heat-source-side heat exchangers 3 a and 3 b, the two-phasegas-liquid refrigerant exchanges heat with air supplied by theair-sending device (not shown) to become gas refrigerant having a lowtemperature and a low pressure. The heat-source-side heat exchangers 3 aand 3 b function as evaporators that receive heat from the ambient airand evaporate the refrigerant in the pipes. After flowing from theheat-source-side heat exchangers 3 a and 3 b, the gas refrigerant flowsinto the accumulator 5 through pipes and the flow-path switching unit 2in the outdoor unit 20. The refrigerant having flown into theaccumulator 5 is separated into liquid refrigerant and gas refrigerant,and the gas refrigerant is sucked into the compressor 1.

When the heating operation is continued at a low external temperature(at an evaporating temperature of 0 degrees C. or less), frost forms onsurfaces of the heat-source-side heat exchangers 3 a and 3 b. This isbecause with moisture contained in air to be subjected to heat exchangeat the heat-source-side heat exchangers 3 a and 3 b, dew condensationoccurs at the surfaces of the heat-source-side heat exchangers 3 a and 3b, which serve as evaporators, and the temperature of outside air islow, as a result of which frost forms. When the quantity of frostforming on the heat-source-side heat exchangers 3 a and 3 b increases,the thermal resistance increases, and the quantity of air decreases.Consequently, pipe temperatures (evaporating temperatures) in theheat-source-side heat exchangers 3 a and 3 b lower, and the heatingcapacity cannot be sufficiently fulfilled. It is therefore necessary toperform defrosting to remove the frost.

[Defrost Operation Mode]

FIG. 3 is a diagram illustrating flows of refrigerant during the defrostoperation of the air-conditioning apparatus. In FIG. 3, flows ofrefrigerant during the defrost operation mode are indicated by arrows.In the defrost operation mode, a normal heating operation is stopped,and the direction of circulation of the refrigerant is changed by theflow-path switching unit 2 to the same direction as that in the coolingoperation mode. When gas refrigerant having a low temperature and a lowpressure is sucked into the compressor 1, it is compressed by thecompressor 1 to become gas refrigerant having a high temperature and ahigh pressure, and is discharged from the compressor 1. The gasrefrigerant discharged from the compressor 1 passes through theflow-path switching unit 2, and flows into the heat-source-side heatexchangers 3 a and 3 b. In the heat-source-side heat exchangers 3 a and3 b, the gas refrigerant having the high temperature and high pressureexchanges heat with the ambient air to become liquid refrigerant. Theheat-source-side heat exchangers 3 a and 3 b function as condensers,which transfer heat to the ambient air and reduce the temperature ofrefrigerant in the pipes. The heat transferred by the heat-source-sideheat exchangers 3 a and 3 b to the air melts the frost on the surfacesof the heat-source-side heat exchangers 3 a and 3 b. At this time, inmany cases, the air-sending device (not shown), which is located closeto the heat-source-side heat exchangers 3 a and 3 b, is in stoppedstate. After flowing from the heat-source-side heat exchangers 3 a and 3b, the liquid refrigerant flows into the indoor units 10 a, 10 b, 10 cand 10 d through the pipe B.

In the indoor units 10 a, 10 b, 10 c and 10 d, the liquid refrigerant isexpanded and reduced in pressure by the respective expansion units 11 a,11 b, 11 c and 11 d to become two-phase gas-liquid refrigerant having alow temperature and a low pressure. The two-phase gas-liquid refrigerantflows from the indoor units 10 a, 10 b, 10 c and 10 d without beingsubjected to heat exchange at the use-side heat exchangers 12 a, 12 b,12 c and 12 d. After flowing from the indoor units 10 a, 10 b, 10 c and10 d, the two-phase gas-liquid refrigerant re-flows into the outdoorunit 20 through the pipe A. In the outdoor unit 20, the two-phasegas-liquid refrigerant passes through the flow-path switching unit 2,and flows into the accumulator 5. The refrigerant having flown into theaccumulator 5 is separated into liquid refrigerant and gas refrigerant,and the gas refrigerant is re-sucked into the compressor 1.

[During Defrost Operation]

FIG. 4 is a schematic diagram of the heat-source-side heat exchanger ofthe air-conditioning apparatus. FIG. 4 illustrates the heat-source-sideheat exchanger 3 a as viewed side-on. FIG. 5 is a diagram illustratingflows of refrigerant in the case where the solenoid valve for the bypassis opened during the defrost operation of the air-conditioningapparatus. The heat-source-side heat exchanger 3 a has a structure thatplural heat transfer tubes bent in a hairpin manner are inserted intoplural fins in a direction perpendicular thereto. The bypass 6 a isprovided to extend through the lower part of the heat-source-side heatexchanger 3 a. Since the heat-source-side heat exchanger 3 a is long ina step direction, there is a possibility that after the defrostoperation, defrost water will be collected in the part of theheat-source-side heat exchanger 3 a through which the bypass 6 a isprovided to extend, and will be refrozen. Therefore, as illustrated inFIG. 5, in the defrost operation or in a last stage of the defrostoperation, the solenoid valve 4 is opened to cause the refrigerant inthe pipe to flow into the bypass 6 a. As described above, during thedefrost operation, the refrigerant in the pipe in the outdoor unit 20has a high temperature and a high pressure. Therefore, by causing therefrigerant to flow into the bypass 6 a, it is possible to enhanceheating of the lower part of the heat-source-side heat exchanger 3 a. Asa result, frost is prevented from being re-frozen at the lower part ofthe heat-source-side heat exchanger 3 a. Similarly, the bypass 6 b isprovided to extend through the lower part of the heat-source-side heatexchanger 3 b, and the solenoid valve 4 is connected to the bypass 6 b.Therefore, by opening the solenoid valve 4 in the late stage of thedefrost operation, the refrigerant having a high temperature and a highpressure flows into the bypass 6 b, and frost is prevented from beingrefrozen at the lower part.

In ordinary cases, the defrost operation is ended when it is confirmedthat the entire frost adhering to the heat-source-side heat exchangers 3a and 3 b is completely melted, on the basis of results of detection bytemperature detection units (not shown) provided at the heat-source-sideheat exchangers 3 a and 3 b. When the defrost operation is ended, theflow-path switching unit 2 is switched, and the operation to beperformed is returned to the above heating operation. It is determinedto end the defrost operation, for example, by detecting an increase inthe temperatures of the pipes in the heat-source-side heat exchangers 3a and 3 b, which is caused by removal of the entire frost.

In order to prevent frost from being refrozen after the defrostoperation, there is a case where it is necessary to consider aninfluence of an environment in which the air-conditioning apparatus 100,which causes refrigerant to be circulated using the bypasses 6 a and 6 bas illustrated in FIG. 5, is installed. In many cases, amulti-air-conditioning apparatus for a building is used in a large-scalebuilding or facility because of its usage, and a large number of outdoorunits are installed on the rooftop. In this description, suchinstallation of the outdoor units of the multi-air-conditioningapparatus for a building is referred to as a dense installation.

FIG. 6 is a diagram showing an example of dense installation of theoutdoor units in embodiment 1 of the present invention. FIG. 6, (a),illustrates a state of the dense installation of the outdoor units asviewed side-on. FIG. 6, (b) to (e), illustrate a state of the denseinstallation of the outdoor units as viewed from above. In FIG. 6, (b)to (e), it is assumed that the front surface of the units are surfacesthereof which faces upward in the figure, and the rear surfaces of theunits are surfaces thereof which face downward in the figure. Also, inthe figure, arrows indicate the directions of wind.

As illustrated in FIG. 6, (a), in the dense installation, in many cases,the intervals at which the outdoor units are arranged laterally are veryshort. Of these outdoor units, in an outdoor unit adjacent to otheroutdoor units on its both sides, the both side surfaces of the outdoorunit respectively face side surfaces of the above adjacent outdoorunits, and the front and rear surfaces of the outdoor unit are exposedto outside air at all times. Also, in the dense installation, one of theside surfaces of each of the outermost ones of the outdoor units faces aside surface of an adjacent outdoor unit, and the other side surface andthe front and rear surfaces of the above each outermost outdoor unit areexposed to outside air at all times. Therefore, the influence of wind onthe outdoor units varies from one outdoor unit to another.

For example, in the case where wind flows as illustrated in FIG. 6, (b),the front surfaces of the outdoor units are more greatly influenced bythe wind than the other surfaces of the outdoor units: and in the casewhere wind flows as illustrated in FIG. 6, (c), the rear surfaces of theoutdoor units are more greatly influenced by the wind than the othersurfaces of the outdoor units. Furthermore, in the case where wind flowsas illustrated in FIG. 6, (d), the left surface of the outermost leftone of the outdoor units as illustrated in the figure is more greatlyinfluenced by the wind than the other surfaces of the outermost leftoutdoor unit and all the surfaces of the other outdoor units, and in thecase where wind flows as illustrated in FIG. 6, (e), the right surfaceof the outermost right one of the outdoor units as illustrated in thefigure is more greatly influenced by the wind than the other surfaces ofthe outermost right outdoor unit and all the surfaces of the otheroutdoor units.

In ordinary cases, in the case where the air-conditioning apparatus isin the cooling operation or the heating operation, the air-sendingdevice is operated to cause wind to forcefully pass through theheat-source-side heat exchangers. However, in the defrost operationdescribed above, the air-sending devices of the outdoor units arestopped. During the defrost operation, if wind flows as illustrated inFIG. 6, (b), a larger amount of outside air comes into contact with thefront surfaces of the outdoor units than the other surfaces thereof, andif wind flows as illustrated in FIG. 6, (c), a larger amount of outsideair comes into contact with the rear surfaces of the outdoor units thanthe other surfaces thereof. Also, during the defrost operation, if windflows as illustrated in FIG. 6, (d), a larger amount of outside aircomes into contact with the left surface of the outermost left one ofthe outdoor units as illustrated in the figure than the other surfacesof the outermost left outdoor unit and all the surfaces of the otheroutdoor units, and if wind flows as illustrated in FIG. 6, (e), a largeramount of outside air comes into contact with the right surface of theoutermost right one of the outdoor units than the other surfaces of theoutermost right outdoor unit and all the surfaces of the other outdoorunits.

In forced convection, a value obtained by multiplying the velocity ofwind by 0.5 is proportional to a thermal conductivity. Therefore, whenthe wind velocity increases by A times, a heat radiation amountincreases by √A times. Therefore, in the defrost operation mode, if windflows as illustrated in FIG. 6, (b) or (c), the heat radiation amountsof the front or rear surfaces of the outdoor units are higher than thoseof the other surfaces of the outdoor units, and heat is removed from thefront or rear surfaces, as a result of which there is a strongerpossibility that defrost water generated by the defrost operation willbe refrozen on the front or rear surfaces. Furthermore, if wind flows asillustrated in FIG. 6, (d), the heat radiation amount of the leftsurface of the outermost left one of the outdoor units as illustrated inthe figure is higher than those of the other surfaces of the outermostleft outdoor unit and all the surfaces of the other outdoor unitsradiation rate, and heat is removed from the left surface of theoutermost left outdoor unit, as a result of which there is a strongerpossibility that defrost water generated by the defrost operation willbe refrozen on the left surface of the outermost left outdoor unit. Ifwind flows as illustrated FIG. 6, (e), the heat radiation amount of theright surface of the outermost right one of the outdoor units asillustrated in the figure is higher than those of the other surfaces ofthe outermost right outdoor unit and all the surfaces of the otheroutdoor units, and heat is removed from the right surface of theoutermost right outdoor unit, and there is a stronger possibility thatdefrost water generated by the defrost operation will be refrozen on theright surface of the outermost right outdoor unit.

Embodiment 1

FIG. 7 is a schematic diagram of a refrigerant circuit of anair-conditioning apparatus according to embodiment 1 of the presentinvention. Structural elements which are the same as those of the aboverefrigerant circuit as illustrated in FIG. 1 to 3 will be denoted by thesame reference signs, and their descriptions will thus be omitted. Inthe air-conditioning apparatus 200 according to embodiment 1, the bypass6 a includes an electronic expansion valve 7 a serving as a flow-rateadjusting mechanism, and a thermistor 8 a serving as a temperaturedetection unit. The electronic expansion valve 7 a and the thermistor 8a are provided on a secondary side of the bypass 6 a, with theheat-source-side heat exchanger 3 a interposed between the electronicexpansion valve 7 a and thermistor 8 a and secondary side of the bypass6 a. Similarly, the bypass 6 b includes an electronic expansion valve 7b serving as a flow-rate adjusting mechanism, and a thermistor 8 bserving as a temperature detection unit. The electronic expansion valve7 b and the thermistor 8 b are provided on a secondary side of thebypass 6 b, with the heat-source-side heat exchanger 3 b interposedbetween the electronic expansion valve 7 b and thermistor 8 b and thesecondary side of the bypass 6 b. A temperature sensor 9 a which detectsan outlet temperature of the heat-source-side heat exchanger 3 a, i.e.,the temperature of an outlet thereof from which refrigerant flows, isprovided at the heat-source-side heat exchanger 3 a; and a temperaturesensor 9 b which detects an outlet temperature of the heat-source-sideheat exchanger 3 b, i.e., the temperature of an outlet thereof fromwhich the refrigerant flows, is provided at the heat-source-side heatexchanger 3 b.

When the solenoid valve 4 is opened, and an opening degree of theelectronic expansion valve 7 a reaches a predetermined opening degree,gas refrigerant having a high temperature and a high pressure starts toflow into the bypass 6 a. After flowing into the bypass 6 a, the gasrefrigerant having the high temperature and high pressure exchanges heatwith defrost water, at the lower part of the heat-source-side heatexchanger 3 a. As a result, while liquefying, the gas refrigerant havingthe high temperature and high pressure heats the bypass 6 a of theheat-source-side heat exchanger 3 a. Thus, the defrost water isprevented from being refrozen. When the solenoid valve 4 is opened, andthe opening degree of the electronic expansion valve 7 b reaches apredetermined opening degree, the gas refrigerant having the hightemperature and high pressure starts to flow into the bypass 6 b. Afterflowing into the bypass 6 b, the gas refrigerant having the hightemperature and high pressure exchanges heat with defrost water, at thelower part of the heat-source-side heat exchanger 3 b. As a result,while liquefying, the gas refrigerant having the high temperature andhigh pressure heats the bypass 6 b of the heat-source-side heatexchanger 3 b. Thus, the defrost water is prevented from being refrozen.

FIG. 8 is a control block diagram of the air-conditioning apparatus 200.A controller 201 controls the entire air-conditioning apparatus 200. Thetemperature sensor 9 a, a temperature sensor 9 b, the thermistor 8 a anda thermistor 8 b are connected to the controller 201. Also, the solenoidvalve 4, the electronic expansion valve 7 a and an electronic expansionvalve 7 b are connected to the controller 201. The controller 201outputs a signal for opening the solenoid valve 4 to the solenoid valve4, when the outlet temperature of the heat-source-side heat exchanger 3a detected by the temperature sensor 9 a becomes a predeterminedtemperature or higher immediately after start of the defrost operationor after elapse of a predetermined time from the start of the defrostoperation. Also, the controller 201 detects the temperature of thethermistor 8 a to determine the opening degree of the electronicexpansion valve 7 a, and outputs a control signal based on the result ofthe determination to the electronic expansion valve 7 a. Similarly, thecontroller 201 outputs a signal for opening the solenoid valve 4 to thesolenoid valve 4, when the outlet temperature of the heat-source-sideheat exchanger 3 b detected by the temperature sensor 9 b becomes thepredetermined temperature or higher. Also, the controller 201 detectsthe temperature of the thermistor 8 b to determine the opening degree ofthe electronic expansion valve 7 b, and outputs a control signal basedon the result of the determination to the electronic expansion valve 7b. To be more specific, the opening degrees of the electronic expansionvalves 7 a and 7 b are determined on the basis of the differences(ΔT=T*+T) between target temperatures T* and the detected temperatures Tof the thermistors 8 a and 8 b, respectively. When ΔT>0, the controller201 outputs control signals for increasing the opening degrees of theelectronic expansion valves 7 a and 7 b, and when ΔT<0, the controller201 outputs control signals for decreasing the opening degrees of theelectronic expansion valves 7 a and 7 b.

As described above, according to embodiment 1, in addition to control ofopening of the solenoid valve 4, control of the opening degrees of theelectronic expansion valves 7 a and 7 b based on the detection resultsof the thermistors 8 a and 8 b is performed, and the flow rates ofrefrigerant to the bypasses 6 a and 6 b are adjusted in accordance withambient environments of the heat-source-side heat exchangers 3 a and 3b. In other words, the defrosting capacities of the heat-source-sideheat exchangers 3 a and 3 b are adjusted in accordance with the ambientenvironments thereof. Therefore, the flow rates of the refrigerant tothe bypasses 6 a and 6 b can be optimized in accordance with defrostingloads on the bypasses 6 a and 6 b. As a result, even if the influencesof wind of outside air upon the surfaces of the heat-source-side heatexchangers 3 a and 3 b vary in accordance with the positions of theoutdoor units in the dense installation as described with reference toFIG. 6, (a) to 6(e), it is possible to reliably prevent defrost waterfrom being refrozen in accordance with the influences.

Embodiment 2

FIG. 10 is a schematic diagram of a refrigerant circuit of anair-conditioning apparatus according to embodiment 2 of the presentinvention. With respect to this embodiment, structural elements whichare the same as those of the refrigerant circuit as illustrated in FIG.1 to 3 will be denoted by the same reference signs, and theirdescriptions will thus be omitted. In an air-conditioning apparatus 300according to embodiment 2, a pipe resistor 15 a is provided in thebypass 6 a, and a pipe resistor 15 b is provided in the bypass 6 b. Thepipe resistors 15 a and 15 b are, for example, capillary tubes. Theinflow rate of refrigerant to the bypass 6 a is determined in accordancewith the pipe resistor 15 a. The inflow rate of the refrigerant to thebypass 6 b is determined in accordance with the pipe resistor 15 b. Flowresistances of the pipe resistors 15 a and 15 b to the flow of therefrigerant are set different from each other to cause the flow rates ofthe refrigerant to the bypasses 6 a and 6 b to differ from each other.

The following description is given by referring to by way of example thecase where the plural outdoor units 20 in the multi-air-conditioningapparatus for a building are densely installed, and wind of outside airflows in the direction indicated in FIG. 6, (b) or (c). FIG. 9 is aschematic diagram illustrating heat-source-side heat exchangers inembodiment 2 of the present invention as viewed from above. Theheat-source-side heat exchangers 3 a and 3 b are L-shaped, and areprovided to form a frame that is substantially rectangular as viewedfrom above in the housing of the outdoor unit 20. The heat-source-sideheat exchanger 3 a is provided on the front surface of the outdoor unit20. In FIG. 9, the front surface of the outdoor unit 20 faces downwardin the figure. Also, referring to FIG. 9, an inlet 13 a and an outlet 13b are an inlet and an outlet of the bypass 6 a of the heat-source-sideheat exchanger 3 a, respectively; and an inlet 14 a and an outlet 14 bare an inlet and an outlet of the bypass 6 b of the heat-source-sideheat exchanger 3 b, respectively. In the case where wind of outside airflows in the direction indicated in FIG. 6, (b) or (c), a surface 16 aof the heat-source-side heat exchanger 3 a is a surface thereof ontowhich the wind flows, and a surface 16 b of the heat-source-side heatexchanger 3 a is a surface thereof onto which the wind flows.

The inlet 13 a of the bypass 6 a of the heat-source-side heat exchanger3 a is located close to the surface 16 a onto which the wind flows.Refrigerant gas having a high temperature flows into part of the surface16 a of the heat-source-side heat exchanger 3 a. On the other hand, theinlet 14 a of the bypass 6 b of the heat-source-side heat exchanger 3 bis located on a side of a side surface thereof which is orthogonal tothe surface 16 b onto which the wind flows. The refrigerant gas passesthrough part of the side surface of the heat-source-side heat exchanger3 b, and flows into part of the surface 16 b. Thus, the temperature ofthe refrigerant gas flowing into the part of the surface 16 b of theheat-source-side heat exchanger 3 b lowers, as compared with thetemperature of the refrigerant gas flowing into the part of the surface16 a of the heat-source-side heat exchanger 3 a. Therefore, thedefrosting capacity of the heat-source-side heat exchanger 3 b needs tobe set higher than the defrosting capacity of the heat-source-side heatexchanger 3 a. In embodiment 2, the flow resistance of the pipe resistor15 b is set lower than the flow resistance of the pipe resistor 15 a.

In such a manner, according to embodiment 2, in the dense installationin the multi-air-conditioning apparatus for a building, in the casewhere it is known which of the defrosting capacities requisite for theheat-source-side heat exchangers 3 a and 3 b of each of the outdoorunits 20 is greater or smaller, pipe resistors 15 a and 15 b whose flowresistances are set in accordance with the requisite defrostingcapacities are provided.

According to embodiment 2, it is possible to reduce increasing of thenumber of components. Therefore, in the dense installation, in the casewhere it is known which of defrosting capacities which are requisite forthe heat-source-side heat exchangers 3 a and 3 b in accordance with theposition of each of installed outdoor units is greater or smaller, thedefrost water at the heat-source-side heat exchangers 3 a and 3 b can beprevented from being refrozen, at the same time as the product cost isreduced.

Reference Signs List  1 compressor  2 flow-path switching unit  3aheat-source-side heat exchanger  3b heat-source-side heat exchanger  4solenoid valve  5 accumulator  6a bypass  6b bypass   7a electronicexpansion valve  7b electronic expansion valve  8a thermistor  8bthermistor  9a temperature sensor  9b temperature sensor  10a indoorunit  10b indoor unit  10c indoor unit  10d indoor unit  11a expansionunit  11b expansion unit  11c expansion unit  11d expansion unit  12ause-side heat exchanger  12b use-side heat exchanger  12c use-side heatexchanger  12d use-side heat exchanger  13a inlet  13b outlet  14a inlet 14b outlet  15a pipe resistor  15b pipe resistor  16a surface 16bsurface  20 outdoor unit 100 air-conditioning apparatus 200air-conditioning apparatus 201 controller 300 air-conditioningapparatus.

1. An air-conditioning apparatus comprising: an outdoor unit including acompressor, a flow-path switching unit and plural heat-source-side heatexchangers, the compressor, the flow-path switching unit and theheat-source-side heat exchangers being connected by pipes; and an indoorunit connected to the outdoor unit to air-condition a target space,wherein the outdoor unit includes: plural bypasses each having ends oneof which is, in connection by pipes in the outdoor unit, connected to adischarge side of the compressor, and the other of which is connected toa suction side of the compressor, the bypasses being configured to causerefrigerant to flow through lower parts of the plural heat-source-sideheat exchangers during a defrost operation of the air-conditioningapparatus; and flow-rate adjusting mechanisms provided in the respectivebypasses to adjust flow rates of refrigerant flowing into the pluralbypasses.
 2. The air-conditioning apparatus of claim 1, wherein theoutdoor unit further comprises a controller and detection unitsconfigured to detect ambient temperatures of the plural heat-source-sideheat exchangers, and the controller controls the flow-rate adjustingmechanisms based on ambient temperatures which are detected by therespective detection units of the plural heat-source-side heatexchangers, and adjusts flow rates of the refrigerant flowing into thebypasses, immediately after start of the defrost operation of theair-conditioning apparatus, or after elapse of a set time from the startof the defrost operation.
 3. The air-conditioning apparatus of claim 2,wherein the flow-rate adjusting mechanisms are electronic expansionvalves, and the controller adjusts opening degrees of the electronicexpansion valves.
 4. The air-conditioning apparatus of claim 1, whereinthe flow-rate adjusting mechanisms are capillary tubes, and the flowrates of the refrigerant flowing into the plural bypasses through thecapillary tubes are set different from each other with respect to theplural heat-source-side heat exchangers.